O.S.H.A. requirements for many industrial machine controls specify that the operator must use both hands to initiate operation of the machine. This requirement was established to prevent possible hand injuries to the machine operator. Most machine control stations of this type employ two palm button mechanical switches. The two palm buttons must close the operating circuit to cause the machine to operate. The force required to press the palm buttons is variable with each palm button, however, it is sufficient enough to give the operator a "tactile feel" indicating to him that the switch has been activated. U.S. Pat. No. 4,412,268 to Dessow discloses an industrial machine control station employing two proximity switches which replicate the function of the more conventional palm button mechanical switches for controlling an industrial machine. In Dassow's device the machine operator is required to touch a sensing plate to operate the machine. The control circuit of Dessow does not provide for proximity switch failure monitoring. It is also noted that the machine control station disclosed in the patent to Dassow has output contacts which are connected in series with the line power to the machine being controlled. As a result, the high current carried by the output contacts significantly increases the chance of welding such contacts closed which could result in the machine being controlled continuing to run after the operator has removed his hands from the operator station. Dassow's output circuit is also controlled by an anti-cheat timer which would appear to provide a pulsed output to the machine. A pulsed output would require adjustment to match the machine's operating time cycle. The patent to Dassow also discloses the provision of proximity switches which are tuned to different frequencies for the purpose of preventing "inadvertent operation as a consequence of operating the first switch", i.e. unintended activation of one of the two proximity switches caused by interference from the other switch. However, the patent to Dassow does not address or even recognize the problem of unintended simultaneous activation of both capacitive proximity switches which is caused by the presence of emitted or conducted radio frequency interference.